Vehicle propulsion systems typically include a transmission for transferring mechanical work from a propulsion device such as an internal combustion engine or electrically powered motor to a drive wheel of the vehicle. These transmissions can be configured to provide a plurality of selectable gear ratios between an input shaft for receiving the mechanical work and an output shaft for delivering the mechanical work to the drive wheel. A transmission controller can be provided for selecting the appropriate transmission gear ratio. In some examples, the controller can adjust the transmission gear ratio via one or more transmission actuators that can manipulate the various transmission elements for effectuating the selected gear ratio by way of a clutch or other suitable device.
One approach for controlling the actuation signal provided to these transmission actuators is described by U.S. Pat. No. 6,262,556. This approach describes how the actuation signal that is provided to an actuator during a transmission shift can be adjusted based on a measured temperature of the transmission's hydraulic fluid. In particular, U.S. Pat. No. 6,262,556 describes how a temperature measured at the transmission sump can be used to select the actuation signal.
However, the inventors herein have identified several issues with the above approach. As one example, the inventors have recognized that measuring the temperature of the hydraulic fluid at only a single location, such as by way of a temperature sensor, provides only a limited indication of transmission temperature during some conditions. For example, during warm-up of the transmission after a cold start, thermal gradients may exist between different regions of the transmission. Furthermore, if the temperature sensing capability of the temperature sensor becomes degraded over time, the transmission may be improperly controlled. Further still, a dedicated transmission temperature sensor can add additional cost and complexity to the transmission.
As such, the inventors herein have addressed some of the above issues by a propulsion system for a vehicle, comprising a propulsion device configured to provide mechanical work via a crankshaft; a transmission having an input shaft coupled with the crankshaft and an output shaft, wherein said transmission includes a plurality of selectable gear ratios between the input and output shaft; at least one drive wheel coupled with the output shaft; an actuation device configured to adjust the selected gear ratio of the transmission; and a control system configured to adjust an electrical signal provided to the actuation device to obtain an indication of a temperature dependent electrical parameter of the actuation device and to adjust the selected gear ratio of transmission by varying the signal provided to the actuation device in response to said indication.
In this way, each actuator of the transmission can be used to provide an indication of temperature, thereby providing a distributed indication of transmission temperature even where temperature gradients exist. Thus, the actuation signal provided to each actuator can be controlled in response to their respective temperature indication and the timing of the actuation as well as the transmission shift points can be more accurately controlled by the transmission control system.
As another example, a method of operating a transmission of a vehicle powertrain including at least a first and a second actuator is provided. The method comprises performing a transmission shift by actuating a first transmission element via the first actuator and actuating a second transmission element via the second actuator; and varying a timing of actuation of the first transmission element relative to the second transmission element based on an indication of a temperature dependant electrical property of at least one of the first actuator and the second actuator.
In this way, two or more actuators of the transmission can be coordinated based on an indication of temperature obtained from an temperature dependant electrical parameter of one or more actuators, such as an electrical resistance of the actuator coil, for example. Furthermore, in some examples, the actuators can be coordinated based on a comparison of their respective temperature indications, thereby enabling smoother and more efficient transmission shifts.